4. Determination of the Phosphorus.10-20 grams of the sample
are dissolved in nitric acid, the excess of the latter expelled, and the liquid
treated with i c.c. of ferric chloride solution free from phosphorus and
rendered alkaline with ammonia. The precipitate is filtered off, washed
and dissolved in hydrochloric acid, and the acid solution treated as described
on p. 174 or, if in presence of arsenic, on p. 176.
5. Determination of the Antimony (Classen).The solution from
which the copper has been removed electrolytically as in i, together with
the washing water from the small beaker, is evaporated until the nitric
acid is completely expelled ; if the anode is brown, it is kept immersed for
some time, a few drops of hydrogen peroxide being added to dissolve the
peroxides deposited on it.1 The solution is diluted with water and sub-
jected to the action of hydrogen sulphide in the cold to prevent the pre-
cipitation of the arsenic. The precipitate is filtered off and washed, and
the antimony oxide and sulphide and any tin oxide and sulphide dissolved
in 80 c.c. of sodium sulphide solution (D 1-225), 4-5 grams of potassium
cyanide being added to the solution and the latter electrolysed in the Classen
dish. ND100 = 0-15 amp. ; duration = 10-15 hours.
6. Determination of the Lead (by electrolysis).5 grams of the
sample are treated with 20-30 c.c. of nitric acid (D 1-18), the nitrous fumes
expelled by boiling and the liquid diluted to 250-300 c.c. and electrolysed,
with a Winkler cathode and a tared gauze cylinder anode, as described on
p. 210. ND100 = 0-51 amp., duration 10-15 hours.
Whilst copper is deposited on the cathode, lead is deposited as peroxide
on the anode. At the end of the electrolysis, the electrodes are removed
and washed with water, and the anode, after further washing with dis-
tilled water, dried at 180-200°, cooled and weighed : Pb02 X 0-866 = Pb.
If manganese and considerable quantities of bismuth and iron are
present, small amounts of the oxides of these metals are deposited on the
anode with the lead peroxide. In such case the deposit is dissolved in
nitric acid containing a little alcohol, the solution being evaporated with
sulphuric acid until copious white fumes appear, the residue being taken
up in water, a little alcohol added, and the lead sulphate separated and
weighed. Another method consists in employing, for the determination
of the lead, the lead sulphate which separates during the necessary pro-
cedure for the electrolytic determination of the bismuth (see 2, a).
7. Determination of the Sulphur.The solution freed from copper
and lead by electrolysis (see 6) is evaporated to dryness (to fix the sulphuric
acid it is advisable to add a little sodium carbonate). The residue is taken
up twice in hydrochloric acid, the liquid being evaporated to dryness each
time to expel the whole of the nitric acid. The final residue is then dis-
solved in 5 c.c. of cone, hydrochloric acid and 50 c.c. of hot water and barium
chloride added to the clear liquid thus obtained to precipitate the sulphuric
acid formed by oxidation of the sulphur during the attack of the metal,
the ordinary conditions being observed.
8. Determination of the Iron, Nickel and Zinc.5 grams of
1 In case the copper has been deposited twice, the solution from the second
deposition must also be added.o